The neural crest is a migratory population of cells that gives rise to a wide range of cell types in the[unreadable] peripheral nervous system of vertebrate embryos. It has been shown that neural crest cells migrate along[unreadable] very specific pathways throughout the embryo. The reason for such specificity is not fully known. During the[unreadable] last years, some known axon pathfinding repellants (ephrinB2, Semallla, Slit2, etc) have been shown to[unreadable] repel neural crest cells during their migration throughout the embryo. However, we know very little about the[unreadable] migratory clues that guide the neural crest for the rest of their path. It is the goal of this study to find which[unreadable] other molecules are capable of guiding the neural crest along their migratory routes.[unreadable] For this purpose I had set out to screen a group of neurotrophic factors that are expressed at the same time[unreadable] that the crest is migrating through the embryo and which have been shown to be important in neural crest[unreadable] migration by analyzing the corresponding knockout mice. I had taken an in vitro and in vivo approach using a[unreadable] battery of commercially available and cell lines as well that secrete NGF, GDNF, NTS and Neuregulins. In[unreadable] the first case, I modified the already classical collagen gel assay, thus culturing early neural tubes in close[unreadable] proximity to cells that secrete neurotrophic factors. I have also tested neurotrophins' effect on neural crest[unreadable] cells in chemotaxis chambers. The prelimminary results suggest that neural crest cells are attracted to[unreadable] GDNF and Neuregulin. I also tested the effect that these factors would have on live developing chicken[unreadable] embryos. I found that NTS and GDNF were capable of disrupting the migration of trunk neural crest cells.[unreadable] These preliminary data suggests that neural crest cells use a variety of neurotrophic factors as guiding clues[unreadable] during their extensive migration in the embryo. The methods I will use in this proposal will be a) in vitro:[unreadable] isolating neural crest cells and expose them to neurotrophins in chemotaxis chambers, focal points of[unreadable] neurotrophins (as done for growth cone guidance) and in the media. B) in vivo: injecting the celsl secreting[unreadable] neurotrophins, electroporating dominant negative forms and siRNA of their receptors and injecting beads[unreadable] coated with neurotrophins along their regular pathways and also on areas that neural crest cells will not[unreadable] populate to test their potency in attracting them to these novel sites.[unreadable] The relevance that this research will have to public health comes from showing which molecules can attract[unreadable] cells during migration, this knowledge can be tranlated into future therapies with stem cells, especially by[unreadable] helping these cells reach the desired targets for proper regeneration. In addition, the success of this project[unreadable] will demonstrate for the first time that neural crest cells are guided by chemoattractants as well as[unreadable] chemorepellant in the formation of the peripheral nervous system.[unreadable]